How do you solve problem when first serve hit the net?

it is a fault and they go on to second serve, on the same side. if a ball hits the top of the net and goes in, it is a let and if that was the first serve it is still first serve, same side, no score change. if the server double faults the other team gets the point, and if on the second serve someone serves a let, it is still second serve, not a fault